Unit I L1 (Ch15)Fluids Pressure,Pressure & Depth

Density = M/V unit: kg / m3 [or g/cm3]

Density of water w = 1000 kg / m3 = 1 g / cm3 = 1 g/ml

1 gallon of water = 3.79 L

the mass of 1 gallon water = _3.79_kg

Is air light or heavy?* comparing the mass of a carton full of eggs in a refrigerator and the mass of the air in the refrigerator.

a) A carton of egg meggs = 12 * (44g) = 0.53 kg

b) In a fridge of 1.0m x 0.60m x 0.75m,the air weighs (air = 1.29 kg/m3)mair = V

= _0.58_ kg

Working with fluid not solid

Pressure PP = F / A unit: N/m2

1 N/m2 = 1 pascal (Pa)

Pressure is increased if Fincrease or if F is applied to a smaller area.

Decreasing pressure by increasing area

A boat made of concrete floats on water

Increasing floating force by increasing area

Popping a balloon Find the pressure exerted on the

skin of a balloon if you press with a force of 2.1 N using

a) your finger (Area = 1.0*10-4 m2)P = _2.1*104__ N/m2

b) a needle (Area = 2.5*10-7 m2)P = _8.4*106 _ N/m2

Atmospheric Pressure - Patm is a direct result of the weight

of the air above us.

Patm = 1.01 * 105 N/m2= 101 kPa

1 bar = 105 Pa 1 PatmGauge Pressure Pg = P - Patm

Force on your palm Find the force exerted on the

palm of your hand by atmospheric pressure, assuming your palm measures 0.080 m by 0.10 m.

F = Patm * A = _8.1*102_ N

Static Equilibrium in Fluids

Pressure and Depth * At a depth h below the surface of a fluid, the pressure P is

P = Patm + ghwhere is the density of the fluid

The Size of Bubbles

Pressure under the deep ocean* The Titanic was found lying on the bottom of the N. Atlantic at a depth of 2.5 miles. What is the pressure at this depth? (take = 1025 kg/m3)

P = Patm + gh= ___4.0 * 107 Pa__ N/m2

Pressure at a depth in a fluid acts equally in all directions, and acts at right angles to any surface

Buoyant force on the block is the difference between the upward and downward forces.

FB = PA P0A= (Patm + g(d+h))A

(Patm + gd)A= ghA= flgVblock= mflg

Pressure P1 depends on which of the followings:

1) volume of the container

2) volume of the block

3) d4) d

d

Pressure and Depth A cubical box 20.00 cm on a side is

completely immersed in a fluid. At the top of the box, P1 is 105.0 kPa, at the bottom P2 is 106.8 kPa. What is the density of the fluid? P1 = Patm + gd

P2 = Patm + g(d+0.2)P2 P1 = g*0.2 = 900 kg/m3

Oil and water does not mix density of the oil is 9.20*102 kg/m3 density of water is 1.00*103 kg/m3 Find height difference h = ?PA = PBwgh1=oilgh2h = h2-h1

= 0.400 cm

#18

h = h2-h1= 0.400 cm

HW L1 Ch15#3#15 #19#25#27

Unit I L2 (Ch15)Fluids Pascals,

Archimedes,Bernoullis

BarometerPat = ghFor mercury (Hg) = 1.3595 *104 kg/m3h = 760 mm

Do Now - Page 532 #28

P due to the weight of water

Pw = wg (1-d) P due to weight of Hg

PHg = Hgg dPw + PHg + Patm= 2Patm 0.72 m

1 meter

d

1- d

Pascals Principle An external pressure applied to an

enclosed fluid is transmitted unchanged to every point within the fluid.

P = Patm + ghP1 = (Patm + P ) + gh

= Patm + gh + P= P + P

Pascals Principle at work hydraulic lift

P1 = P2= P1 F1 / A1F2 = P2 * A2F1 / F2 = A1 / A2F1 = F2 * A1/A2F1 / A1 = F2 / A2

Hydraulic lift To inspect a 1,200-kg car, it is

raised with a hydraulic lift. If the radius of the small piston is 4.0 cm, and the radius of the large piston is 17 cm, find the force that must be exerted on the small piston to lift the car. F1 = _6.5*102_ N

Fluid flow and continuityA1v1 = A2v2

Ideal fluid: incompressible & nonviscous

Bernoullis equationP1 + v12 + gy1 = P2+ v22 + gy2- higher v is associated with lower P

Airplane liftBernoullis principle in action

Archimedes Principle & Buoyancy

An object immersed in a fluid experiences an upward buoyant force equal in magnitude to the weight of fluid displaced by the object. Fb = fluid gVblock

Volume of fluid displaced

Comparing buoyant force 1Two cubic blocks have the same

dimension but are made of different materials. One is made of steel, the other of wood. When dropped into a cup filled with water, both cubes will sink. Which cube will experience greater buoyant force?

the same

Comparing buoyant force 2Two cubic blocks have the same

dimension. One block is made of styrofoam, and the other is made of balsa wood. When dropped into a cup filled with water, both cubes float. Which block experiences greater buoyant force?styrofoam =100 kg/m3 balsa = 120 kg/m3 Balsa wood

Archimedes principle* A flask of water rests on a scale. If you dip your finger into the water, without touching the flask, does the reading on the scalea) increaseb) decreasec) stay the same. increase

Measuring body densityAs shown in the figure, the weight of the person in air is W = mg = 720.0 N, and the apparent weight in water is Wa = 34 N. Find volume of the person, & his density.

Fb = W - Wa = wgVVp = 6.99 * 10-2 m3pp =m/Vp

=1050 kg/m3

What percentage of the icebergs volume is under water?%= 90%

ice= 920 kg/m3 sea-water= 1025 kg/m3

Find tension in the string A piece of wood with a density of 706

kg/m3 is tied with a string to the bottom of a water-filled flask. The wood is completely immersed, and has a volume of 8.00 * 10-6 m3.

What is the tension in the string?

T + mg = FbT = Fb mg = 0.024 N

Co-meeting work- complete and hand inchapter 15#32#34#44

#34 (5.3 kN)1. FBD2. F=maFb = WHe+Wload+WballonairgV = HegV+Wload+mballong Wload

WHe Wballoon

HW L2 Ch15#33#35#43 #47This homework will be checked for work.